WO2010002796A2 - Absolute elemental concentrations from nuclear spectroscopy - Google Patents
Absolute elemental concentrations from nuclear spectroscopy Download PDFInfo
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- WO2010002796A2 WO2010002796A2 PCT/US2009/049070 US2009049070W WO2010002796A2 WO 2010002796 A2 WO2010002796 A2 WO 2010002796A2 US 2009049070 W US2009049070 W US 2009049070W WO 2010002796 A2 WO2010002796 A2 WO 2010002796A2
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- subterranean formation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V5/00—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity
- G01V5/04—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging
- G01V5/08—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging using primary nuclear radiation sources or X-rays
- G01V5/10—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging using primary nuclear radiation sources or X-rays using neutron sources
- G01V5/101—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging using primary nuclear radiation sources or X-rays using neutron sources and detecting the secondary Y-rays produced in the surrounding layers of the bore hole
Definitions
- the present disclosure relates generally to neutron-induced gamma-ray spectroscopy and, more particularly, to techniques for determining absolute elemental concentrations from neutron-induced gamma-ray spectroscopy.
- the elemental concentration of a subterranean formation may be determined using a variety of techniques.
- An indirect determination of formation lithology may be obtained using information from density and photoelectric effect (PEF) measurements from gamma-ray scattering in the formation.
- a direct detection of formation elements may be obtained by detecting neutron-induced gamma- rays.
- Neutron-induced gamma-rays may be created when a neutron source emits neutrons into a formation, which may interact with formation elements through inelastic scattering, high-energy nuclear reactions, or neutron capture.
- Gamma-rays emitted in inelastic scattering events (“inelastic gamma-rays") or neutron capture events (“neutron capture gamma-rays”) may have characteristic energies that, based on various spectroscopy techniques, may identify the particular isotopes that emitted the gamma-rays.
- Techniques involving inelastic spectroscopy interpretation may be based on ratios of elemental yields attributable to inelastic gamma-rays of various characteristic energies. Most notably, the ratio of the number of detected gamma-rays due to carbon versus those due to oxygen (“C/O ratio”) has been used to estimate formation oil saturation.
- An advantage of using a ratio is that some instrumental effects, such as variable neutron output and a number of environmental effects, will cancel out.
- a disadvantage of using a ratio is that it is usually more difficult to interpret. For the simple case of estimating oil saturation in a water-filled borehole, the C/O ratio may be complicated by gamma-rays attributable to oxygen from borehole fluid and the cement annulus, whereas all gamma-rays attributable to carbon would derive from the formation.
- Similar techniques involving neutron capture spectroscopy may involve collecting and analyzing neutron gamma ray energy spectra.
- Elements typically included in a neutron capture spectrum may include Si, Ca, Fe, S, Ti, Gd, H, Cl, and others, and sometimes Al, Na, Mg, Mn, Ni, and other minor or trace elements.
- the elemental concentrations determined using such techniques may also generally identify only relative concentrations of formation elements, unless an absolute concentration of a formation element is already known or properly estimated.
- Certain other techniques for estimating absolute elemental concentrations in a formation may involve oxide closure normalization of spectroscopy log data, or may involve supplementing spectroscopy log data with activation and/or natural gamma- ray measurements.
- closure normalization may depend on accurate associations for unmeasured elements, which may change depending on the exact assembly of formation elements. Additionally, closure normalization may depend on using all elements that may influence the spectrum (except K and Al), some of which may not be as precisely determined as others.
- the use of activation and/or natural gamma-ray measurements may also have various disadvantages. In particular, such measurements may often involve highly complex tools and long measurement times.
- a system for estimating an absolute yield of an element in a subterranean formation may include a downhole tool and data processing circuitry.
- the downhole tool may include a neutron source to emit neutrons into the formation, a neutron monitor to detect a count rate of the emitted neutrons, and a gamma-ray detector to obtain gamma-ray spectra deriving at least in part from inelastic gamma- rays produced by inelastic scattering events and neutron capture gamma-rays produced by neutron capture events.
- the data processing circuitry may be configured to determine a relative elemental yield from the gamma-ray spectra and to determine an absolute elemental yield based at least in part on a normalization of the relative elemental yield to the count rate of the emitted neutrons.
- FIG. l is a schematic block diagram of a system including a downhole tool and data processing circuitry for measuring absolute elemental concentrations based on spectral analysis of neutron- induced gamma-rays, in accordance with an embodiment
- FIG. 2 is a schematic block diagram of a well logging operation using the downhole tool of FIG. 1 , in accordance with an embodiment
- FIG. 3 is a flowchart describing an embodiment of a method for determining absolute elemental yields in a formation based on neutron-induced gamma-ray measurements, in accordance with an embodiment
- FIG. 4 is a flowchart describing an embodiment of a method for determining partial absolute elemental yields in a formation and a borehole based on neutron- induced gamma-ray measurements, in accordance with an embodiment
- FIG. 5 is a flowchart describing an embodiment of a method for determining absolute elemental concentrations based on determined absolute elemental yields, in accordance with an embodiment
- FIG. 6 is a flowchart describing an embodiment of a method for verifying the absolute elemental concentrations using oxide-closure techniques and relative yields, in accordance with an embodiment.
- Embodiments of the presently disclosed subject matter relate generally to systems and methods for neutron-induced gamma-ray spectroscopy.
- the presently disclosed subject matter relates to techniques for determining absolute elemental concentrations of a subterranean formation. These techniques may involve causing inelastic scattering events and neutron capture events in a subterranean formation by bombarding the formation with neutrons, which may cause the emission of inelastic and neutron capture gamma-rays.
- the inelastic and neutron capture gamma-rays may have energy spectra that are characteristic to the elements from which they derive.
- the quantity of emitted neutrons may be monitored or otherwise known, and the resulting gamma-ray spectra may be measured and normalized to the monitored neutron output. It has been determined that estimates of the absolute elemental concentrations can be derived from the absolute gamma-ray spectroscopy elemental yields, which may be refer to the gamma-ray spectroscopy yield normalized by the monitored or known neutron output and various environmental corrections to account for formation and/or borehole properties. As used herein, the term "absolute yields" is not meant to imply that the gamma-ray spectroscopy measurement is carried out with reference to a known formation element. Rather, no direct measurement of other elements may be needed to derive an empirical closure factor according to the techniques described below.
- FIG. 1 illustrates a system 10 for determining absolute elemental concentrations of a subterranean formation that includes a downhole tool 12 and a data processing system 14.
- the downhole tool 12 may be a slickline or wireline tool for logging an existing well, or may be installed in a borehole assembly for logging while drilling (LWD).
- the data processing system 14 may be incorporated into the downhole tool 12 or may be at a remote location.
- the downhole tool 12 may be surrounded by a housing 16.
- the downhole tool 12 may include a neutron source 18 configured to emit neutrons into a subterranean formation.
- the neutron source 18 may be an electronic neutron source, such as a MinitronTM by Schlumberger Technology Corporation, which may produce pulses of neutrons through d-D and/or d-T reactions. Additionally or alternatively, the neutron source 18 may be a radioactive source, such as an AmBe or 252 Cf source.
- the neutron output of the neutron source 18 may be known through the use of various techniques. For example, if the neutron source 18 includes a radioactive source, the absolute output of the neutron source 18 may be determined through calibration. Additionally, the absolute output of the neutron source 18 may be determined by computing the change of neutron source 18 activity as a function of the time since a calibration, since a radioactive source may follow a known exponential decay law and may have a known half-life.
- a given instantaneous output of the neutron source 18 may depend upon many parameters that control the generation of neutrons and, thus, the neutron output of the neutron source 18. These parameters may include the ion beam current supplied inside the neutron generator tube, the accelerating high voltage applied to the tube, and the operation of the ion source, among other things. However, even if all of these parameters are closely regulated, a constant neutron output may not be assured, as short term fluctuations in neutron output may arise due to changes in neutron generator operating characteristics with time and temperature. Additionally, longer term changes due to the aging of the generator tube may further impact the neutron output of the neutron source 18.
- a neutron monitor 20 may monitor the neutron output from the neutron source 18.
- the neutron monitor 20 may be, for example, a plastic scintillator and photomultiplier that may primarily detect unscattered neutrons directly from the neutron source 18, and may provide a count rate signal proportional to the neutron output rate from the neutron source 18.
- the neutron output whether determined through calibration of the neutron source 18 and/or appropriate calculations, or through the use of the neutron monitor 20, may be used for determining absolute spectral yields attributable to various formation elements.
- a neutron shield 22 may separate the neutron source 18 from various detectors in the downhole tool 12.
- a similar shield 24, which may contain elements such as lead, may prevent gamma-rays from traveling between the various detectors of the downhole tool 12.
- the downhole tool 12 may further include one or more gamma-ray detectors, and may include three or more gamma-ray detectors.
- the downhole tool 12 illustrated in FIG. 1 includes two gamma-ray detectors 26 and 28. The relative positions of the gamma-ray detectors 26 and/or 28 in the downhole tool 12 may vary.
- the gamma-ray detectors 26 and/or 28 may be contained in respective housings 30.
- Scintillator crystals 32 in the gamma-ray detectors 26 and/or 28 may enable detection counts or spectra of gamma-rays by producing light when gamma- rays scatter or are captured in the scintillator crystals 32.
- the scintillator crystals 32 may be inorganic scintillation detectors containing, for example, NaI(Tl), LaCl 3 , LaBr3, BGO, GSO, YAP, and/or other suitable materials.
- Housings 34 may surround the scintillator crystals 32.
- Photodetectors 36 may detect light emitted by the scintillator crystals 32 when a gamma-ray is absorbed and the light has passed through an optical window 38.
- the gamma-ray detectors 26 and/or 28 may be configured to obtain a gamma-ray count and/or gamma-ray spectra, and may thus include a gamma-ray pulse height analyzer.
- One or more neutron detectors 21 may be located elsewhere in the downhole tool 12, and may be used for determining various environmental correction factors, as described below.
- the one or more neutron detectors 21 may be thermal, epithermal, or fast neutron detectors that may allow measurement of a dependence on the thermal and/or epithermal neutron flux in the vicinity of the gamma-ray detectors 26 and/or 28. This thermal and/or epithermal neutron flux may be measured or estimated by the one or more neutron detectors 21 located away from the neutron source 18.
- the signals from the neutron monitor 20, the one or more neutron detectors 21, and gamma-ray detectors 26 and/or 28 may be transmitted to the data processing system 14 as data 40 and/or may be processed or preprocessed by an embedded processor in the downhole tool 12.
- the data processing system 14 may include a general-purpose computer, such as a personal computer, configured to run a variety of software, including software implementing all or part of the present techniques.
- the data processing system 14 may include, among other things, a mainframe computer, a distributed computing system, or an application-specific computer or workstation configured to implement all or part of the present technique based on specialized software and/or hardware provided as part of the system.
- the data processing system 14 may include either a single processor or a plurality of processors to facilitate implementation of the presently disclosed functionality.
- the data processing system 14 may include data processing circuitry 44, which may be a microcontroller or microprocessor, such as a central processing unit (CPU), which may execute various routines and processing functions.
- CPU central processing unit
- the data processing circuitry 44 may execute various operating system instructions as well as software routines configured to effect certain processes and stored in or provided by a manufacture including a computer readable-medium, such as a memory device (e.g., a random access memory (RAM) of a personal computer) or one or more mass storage devices (e.g., an internal or external hard drive, a solid- state storage device, CD-ROM, DVD, or other storage device).
- a computer readable-medium such as a memory device (e.g., a random access memory (RAM) of a personal computer) or one or more mass storage devices (e.g., an internal or external hard drive, a solid- state storage device, CD-ROM, DVD, or other storage device).
- the data processing circuitry 44 may process data provided as inputs for various routines or software programs, including the data 40.
- Such data associated with the present techniques may be stored in, or provided by, the memory or mass storage device of the data processing system 14.
- data may be provided to the data processing circuitry 44 of the data processing system 14 via one or more input devices.
- data acquisition circuitry 42 may represent one such input device; however, the input devices may also include manual input devices, such as a keyboard, a mouse, or the like.
- the input devices may include a network device, such as a wired or wireless Ethernet card, a wireless network adapter, or any of various ports or devices configured to facilitate communication with other devices via any suitable communications network, such as a local area network or the Internet.
- the data processing system 14 may exchange data and communicate with other networked electronic systems, whether proximate to or remote from the system.
- the network may include various components that facilitate communication, including switches, routers, servers or other computers, network adapters, communications cables, and so forth.
- the downhole tool 12 may transmit the data 40 to the data acquisition circuitry 42 of the data processing system 14 via, for example, a telemetry system communication downlink or a communication cable.
- the data acquisition circuitry 42 may transmit the data 40 to data processing circuitry 44.
- the data processing circuitry 44 may process the data 40 to ascertain one or more properties of a subterranean formation surrounding the downhole tool 12. Such processing may involve, for example, one or more techniques for estimating absolute yields of formation elements based on absolute inelastic and/or neutron capture gamma-ray spectral yields.
- the data processing circuitry 44 may thereafter output a report 46 indicating the one or more ascertained properties of the formation.
- the report 46 may be stored in memory or may be provided to an operator via one or more output devices, such as an electronic display and/or a printer.
- FIG. 2 illustrates a neutron-induced gamma-ray well-logging operation 48, which involves the placement of the downhole tool 12 into a surrounding subterranean formation 50.
- the downhole tool 12 has been lowered into a borehole 52.
- the well-logging operation 48 may begin when the neutron source 18 outputs neutrons 54 into the surrounding formation 50. If the neutron source 18 emits neutrons of approximately 14.1 MeV, for example, the 14.1 MeV neutrons may collide with nuclei in the surrounding formation 50 through inelastic scattering events 56, which may produce inelastic gamma-rays 58 and may cause the neutrons of the burst of neutrons 54 to lose energy.
- neutrons 54 lose energy to become epithermal and thermal neutrons, they may be absorbed by formation 50 nuclei in neutron capture events 60, which may produce neutron capture gamma-rays 62. If the neutron source 18 emits only neutrons 54 of an energy insufficient to result in inelastic scattering events, substantially only neutron capture events 60 may occur.
- the inelastic gamma-rays 58 and/or neutron capture gamma-rays 62 may be detected by the gamma-ray detectors 26 and/or 28.
- the spectra of the gamma-rays 58 and 62 may be characteristic to the elements from which they derive. As such, the spectra of the gamma-rays 58 and/or 62 may be analyzed to determine elemental yields.
- the neutron monitor 20 near the neutron source 18 may measure the absolute neutron output of the neutron source 18.
- a relationship between the detected gamma-ray 58 and/or 62 spectra and the absolute neutron output of the neutron source 18 may indicate an absolute elemental yield.
- the gamma-ray detectors 26 and/or 28 may generally only be capable of detecting inelastic gamma-rays 58 and/or neutron capture gamma-rays 62 that arise in a certain region of the formation 50 proximate to the respective gamma-ray detector 26 or 28.
- a fraction of the total neutron 54 flux may escape from such regions, and this fraction may depend on various environmental factors.
- fewer neutrons 54 reach the region of the formation 50 that the gamma-ray detectors 26 and/or 28 are sensitive to fewer detectable gamma- rays 58 and/or 62 may be produced. Slowing-down length is one factor that may contribute to this effect.
- the neutron count rate measured by the one or more neutron detectors 21 may need to be corrected for geometrical effects on the variation of neutron flux in the region of the formation 50 that the gamma-ray detectors 26 and/or 28 are sensitive to. Additional measurements from other tools and/or modeling may be used to estimate the fraction of lost neutrons 54, as well as changes in the effective solid angle of the gamma-ray detectors 26 and/or 28. Several factors may contribute to this effect, many of which may be accounted for using various parameters, as described below.
- Another complication that may arise may be specific to the measurement of neutron capture gamma-rays 62.
- the quantity of thermal neutrons that reach the volume of the formation 50 detectable by the gamma-ray detectors 26 and/or 28 may not be directly proportional to the absolute neutron output of high- energy (e.g., 14.1 MeV) neutrons. Rather, the thermal neutron flux may depend on the neutron transport and lifetime of the thermal neutrons through the formation 50 prior to capture.
- additional measurements from other tools and/or modeling may be used to estimate the fraction of thermal neutrons that reach the volume of the formation 50 detectable by the gamma-ray detectors 26 and/or 28.
- One factor in such a calculation may be a sigma measurement of the formation 50, which represents a macroscopic thermal neutron capture cross-section of the formation 50.
- the attenuation of the gamma-rays 58 and/or 62 may also be affected by the environment of the formation 50. As this gamma-ray attenuation may be influenced by a formation density of the formation 50, such a measurement may be used to account for these effects.
- the presence of the borehole 52 may also complicate the obtained measurements of the gamma-rays 58 and/or 62 by the gamma-ray detectors 26 and/or 28.
- the environmental effects of the borehole 52 may be accounted for using additional measurements of borehole 52 parameters and/or modeling, which may include borehole 52 diameter and/or a measurement or estimation of the sigma of the borehole 52.
- the downhole tool 12 includes a neutron detector 21 proximate to the gamma-ray detector 26 and/or 28, this neutron detector 21 may be used to measure the thermal and/or epithermal neutron flux associated with the region of the formation 50 and/or borehole 52 detectable by the gamma-ray detector 26 and/or 28. These measurements may reveal certain formation 50 environmental characteristics, which may be corrected for using the techniques described below.
- FIGS. 3 and 4 represent various embodiments of methods for determining absolute elemental yields from detected gamma-ray spectra.
- the techniques described in FIGS. 3 and 4 represent techniques that may involve the use of the downhole tool 12 and/or the data processing system 14.
- a flowchart 64 begins with step 66, when the downhole tool 12 is lowered into the formation 50 and the neutron source 18 of the downhole tool 12 emits neutrons 54 into the surrounding formation 50.
- step 68 which may take place concurrently with step 66, the absolute neutron output of the neutron source 18 may be measured using the neutron monitor 20 near the neutron source 18.
- the absolute neutron output of the neutron source 18 may be estimated at a later time based on neutron source 18 calibration and radioactive decay models.
- the gamma-ray detectors 26 and/or 28 may measure the spectra of inelastic and neutron capture gamma-rays 58 and/or 62 that may be produced when the neutrons 54 interact with the formation 50.
- Steps 71-76 may generally involve processing steps that may take place in a processor embedded in the downhole tool 12 and/or in the data processing system 14.
- the measured gamma-ray spectra may be divided into elemental contributions, or relative elemental yields.
- these relative elemental yields from gamma-rays attributable to a spectral region of interest may be normalized to the neutron output of the neutron source 18, which may produce an uncorrected absolute elemental yield of the formation 50.
- various factors may be considered to correct for environmental effects of the formation 50 and/or the borehole 52 that may influence the measured gamma-ray 58 and/or 62 spectra.
- one or more absolute elemental concentrations of the formation 50 may be determined, as described below with reference to Equation (1). These steps may be accomplished in any order, and may begin by calculating, for example, the following relationship:
- a 1 Y 1 * TotCR * F(parameter-1, parameter-2, .%) / nCR (1).
- a 1 represents the absolute yields for each element i.
- Y 1 represents the relative elemental yields, or the fraction of the measured gamma-ray spectra attributed to element i.
- TotCR represents the total count rate within the region of the spectrum used in the spectral analysis to extract the relative yields.
- nCR represents the determined neutron 54 output from the neutron source 18, as obtained through an absolute neutron count measurement by the neutron monitor 20 and/or through estimation by calibration or radioactive decay models.
- F represents an environmental correction factor accounting for borehole 52 and/or formation 50 parameters. As mentioned above, such environmental corrections may account for neutron transport and gamma-ray attenuation, among other things. These environmental corrections and parameters are discussed in greater detail below.
- a flowchart 78 describes an embodiment of a method for determining partial absolute yields of elemental concentrations in the formation 50 and the borehole 52.
- the flowchart 78 begins with step 80, when the downhole tool 12 is lowered into the formation 50 and the neutron source 18 of the downhole tool 12 emits neutrons 54 into the surrounding formation 50.
- step 82 which may take place concurrently with step 80, the absolute neutron output of the neutron source 18 may be measured using the neutron monitor 20 near the neutron source 18. Additionally or alternatively, the absolute neutron output of the neutron source 18 may be estimated at a later time based on neutron source 18 calibration or radioactive decay models.
- the gamma-ray detectors 26 and/or 28 may measure the spectra of inelastic and neutron capture gamma-rays 58 and/or 62 that may be produced when the neutrons 54 interact with the formation 50.
- Steps 85-92 may generally involve processing steps that may take place in a processor embedded in the downhole tool 12 and/or in the data processing system 14.
- the measured gamma-ray spectra may be divided into elemental contributions, or relative elemental yields.
- these relative elemental yields from gamma-rays attributable to a spectral region of interest may be normalized to the neutron output of the neutron source 18, which may produce an uncorrected absolute elemental yield of the formation 50.
- step 88 relative yields attributable to the formation 50 and the borehole 52 may be distinguished, and in step 90, various factors may be considered to correct for environmental effects of the formation 50 and/or the borehole 52 that may influence the measured gamma-ray 58 and/or 62 spectra.
- step 92 the partial absolute environmental yields attributable to the formation 50 and the borehole 52 may be determined, as described below with reference to Equation (2).
- the measured absolute yield A 1 may be considered a sum over the partial absolute yields in the formation 50 Ap 1 and the borehole 52 Asm. Under such conditions, it may be possible to distinguish between two possibilities, that there may be a significant spectral difference between the portions of the gamma-ray 58 and/or 62 spectrum arising from the formation 50 and from the borehole 52, and that there may be no usable detectable difference.
- a practical implementation may use either of the two standards separately, or may use the formation 50 standard and the difference between formation 50 and borehole 52 standard. In such a case, the correction factor F may also be split for formation and borehole section independently.
- the steps 85-92 may be accomplished in any order, and may begin by calculating, for example, the following relationship:
- a 1 represents the absolute yields for each element i
- Ap 1 and A BHI represent the partial absolute yields of the element i in the formation 50 and borehole 52, respectively.
- Y F1 and Y BHI represent the relative elemental yields of the formation 50 and borehole 52, or the fraction of the measured gamma-ray spectra attributed to element i attributable to the formation 50 and borehole 52, respectively.
- TotCR represents the total count rate within the region of the spectrum used in the spectral analysis to extract the relative yields.
- nCR represents the determined neutron 54 output from the neutron source 18, as obtained through an absolute neutron count measurement by the neutron monitor 20 and/or through estimation by calibration or radioactive decay models.
- Fp and F BH represent environmental correction factors accounting for formation 50 and borehole 52 parameters, respectively.
- the environmental correction factor(s) F may be a rather complicated function.
- the environmental correction factor(s) F may be factorized, and the dependence on most of the parameters may be determined through a series of Monte Carlo calculations.
- the environmental correction factor(s) F may also include a scaling factor determined by calibration of the final downhole tool 12 hardware. Additionally or alternatively, the scaling factor could be determined from a self-consistency analysis from the results of the closure normalization described above by Equations (1) or (2). An example of a scaling factor is provided below.
- the parameters employed by the environmental correction factor(s) F can be either common physical parameters measured, for example, by other sections of the downhole tool 12 designed for such a purpose, or by other tools.
- such common physical parameters may include, among other things, porosity measurements or estimations, slowing-down time measurements or estimations, density measurements or estimations, formation or borehole thermal neutron capture cross section measurements or estimations, and so forth.
- One or more other parameters may derive from a different set of physical parameters not commonly reported by logging tools, which may have no explicit physical interpretation.
- such other parameters may include, among other things, local neutron flux estimates proximate to the gamma-ray detectors 26 and/or 28, local neutron energy distribution estimates proximate to the gamma-ray detectors 26 and/or 28, raw neutron monitor 20 count rates, raw gamma-ray detector 26 and/or 28 count rates, and so forth.
- These other parameters may involve measurements using the one or more neutron detectors 21 located more closely to the gamma-ray detectors 26 and/or 28 than to the neutron source 18.
- One or more of the factors F applied to the neutron capture gamma-ray 62 yield may contain a dependence on the thermal neutron flux in the vicinity of the gamma-ray detector 26 and/or 28.
- One implementation of such a factor F may contain a fraction between thermal neutron flux near the gamma-ray detector 26 and/or 28 and a measured neutron 54 flux, as measured by the one or more neutron detectors 21 and/or as estimated based on other formation 50 measurements.
- One or more of the factors F applied to the inelastic gamma-ray 58 yield may contain a dependence on the epithermal neutron flux in the vicinity of the gamma-ray detector 26 and/or 28.
- the thermal and/or epithermal neutron flux could be measured or estimated by one or more neutron monitors 20 away from the neutron monitor near the neutron source 18, or may be estimated based on other formation 50 measurements.
- One or more of the factors F may contain a dependency on the gamma-ray attenuation in the vicinity of the gamma-ray detector 26 and/or 28.
- One or more of the factors F may contain a correction for variations in the gamma-ray attenuation in the tool housing 16, which may be due to environmental changes and/or wear.
- One or more of the factors F may contain a correction for downhole tool 12 background resulting from, for example, neutron capture events 60 that may occur in the materials that make up the downhole tool 12.
- One or more of the factors F may contain an estimate of the effective atomic number of the elements in the vicinity of the gamma- ray detector 26 and/or 28, as determined through other downhole measurements or using various other formation 50 modeling techniques.
- Equation (3) One example of a formulation of the correction factor F is described below as Equation (3).
- gi and g 2 depend on D B
- g3 depends on L s
- g 4 depends on ⁇ B .
- FIG. 5 depicts a flowchart 96 for obtaining an elemental concentration of the formation 50.
- the steps of the flowchart 96 may generally involve processing that may take place in a processor embedded in the downhole tool 12 and/or in the data processing system 14.
- a first step 96 may involve obtaining an absolute yield of an element or a partial yield of an element, which may be determined according to the flowcharts 64 or 78 of FIGS. 3 or 4.
- step 98 characteristics specific to the element being assessed may be accounted for and applied to the absolute yield of the element.
- step 100 various physical properties of the element, environment, and/or tool may be accounted by applying a proper scaling factor.
- step 102 based on the above considerations, a partial density of the element in the formation 50 may be obtained.
- steps 96-102 may involve processing that may take place in a processor embedded in the downhole tool and/or in the data processing system 14. Specifically, steps 96-102 may be carried out by calculating, for example, Equation (4) below.
- Equation (4) The partial density for a given element i may be described as follows:
- Si the element-dependent sensitivity that accounts for, among other things, cross sections, gamma-ray multiplicities, gamma-ray detector 26 and/or 28 response, and/or atomic weight, and f is a scaling factor.
- the scaling factor f may be a constant determined from a first principle calculation, which may be derived from the physical constants of the particular element (e.g., mass) and/or other physical information of the environment (e.g., bulk density). Additionally or alternatively, the scaling factor f may be derived, or contain a fraction, from a calibration against measurements under certain predetermined or well-known conditions. In one embodiment, the factor f may be a constant with formation 50 depth.
- the scaling factor f may be a function, rather than a constant. Effects that may be accounted for by employing the scaling factor f as a function may include, for example, remaining instrumental effects like gamma-ray detector 26 and/or 28 drifts and/or resolution degradation. Additionally or alternatively, such effects may further include environmental effects that have not been previously accounted for in the computation of absolute yields A 1 , from the measured raw data. By way of example, environmental effects that arise from temperature and/or pressure, and which have not been accounted for among the factors F in Equations (1) or (2), may be accounted for by employing a scaling factor function f that accounts for such effects.
- the determined partial elemental densities of the formation 50 may be verified using a variety of techniques.
- the sum of all measureable partial densities ⁇ I (P F , I ) correlated with the formation 50 may be smaller than or equal to the bulk density pb, eff of the formation 50, as described by the following relationship:
- the sum of all measurable partial densities ⁇ I (P F , I ) will be smaller than the bulk density pb, eff of the formation 50 in most cases.
- the determined elemental concentration results based on absolute yields A 1 may be checked for consistency using techniques involving relative yields. Specifically, in a first step 106, an elemental concentration of the formation 50 may be determined based on the techniques involving absolute yields, as described above. In a second step 108, the elemental concentration of the formation 50 may be determined based on techniques involving elemental closure or oxide closure with relative yields, as described below with reference to Equations (6) and (7), and/or Equation (8). In step 110, the elemental concentration may be verified.
- the verification step 110 may involve combining the elemental concentration determined based on relative yields with the elemental concentration determined based on absolute yields to obtain a weighted mean of the results, where the weighting may be constant or adjusted based on confidence estimates.
- Such techniques for oxide closure may be used as a secondary estimate of elemental concentrations to verify the calculated partial densities P 1 based on absolute yields A 1 , as described above.
- the oxide closure procedure may utilize neutron capture spectroscopy data along with independent measurements of aluminum (Al) and potassium (K).
- Al aluminum
- K potassium
- the model may assume that the formation 50 elements detected by the neutron capture spectroscopy measurements can be quantitatively linked to their oxides or a most common form in the formation, and that all the oxides will sum to unity.
- the model takes the form of the following relationship:
- W is the weight fraction of the element in the formation
- Y is the relative yield of the element derived from the capture spectrum
- S is a pre-determined measurement sensitivity that depends on the capture cross section of the specific element and the sensitivity of the tool to the characteristic radiation of that element.
- W 1 F x Y 1 / S 1 (7).
- the approach described above may be used for spectra resulting from the inelastic gamma-rays 58.
- several elements can be measured using inelastic spectral yields. These yields can be described as absolute elemental yields using normalization to the neutron source 18 output. Elements like Al, Mg, Ca, Si, S may be present in both the inelastic gamma-ray 58 and neutron capture gamma-ray 62 spectra.
- the use of absolute, environmentally corrected yields makes it possible to combine the results from inelastic gamma-ray 58 and neutron capture gamma-ray 62 spectra or to use the inelastic spectra as a standalone solution.
- inelastic absolute yields and inelastic relative yields due to inelastic gamma-rays 58 can be compared and, where appropriate, combined in a weighted average yield. Additionally, the absolute inelastic yields due to inelastic gamma-rays 58 and the neutron capture yields due to neutron capture gamma-rays 62 for elements present in both inelastic and capture spectra can be used to improve the accuracy and precision of the above answer.
- the environmental corrections for the inelastic yields also may be simpler, as the inelastic yields may be unaffected by the thermal neutron capture cross section of the formation 50 or the borehole 52. This makes inelastic yields particularly valuable in the presence of high borehole 52 salinity and an associated high neutron capture cross section.
- a second closure model may be employed for verifying the calculated partial densities P 1 based on absolute yields A 1 , which may be specifically used in cases where only neutron capture spectroscopy data are available, which may be described in U.S. Patent No. 5,471,057, "METHOD AND APPARATUS FOR DETERMINING ELEMENTAL CONCENTRATIONS FOR GAMMA RAY SPECTROSCOPY TOOLS," which is incorporated by reference herein in its entirety.
- This model may be identical to the model illustrated by Equations (6) and (7) above, except that it eliminates the aluminum (Al) and potassium (K) terms. Additionally, this model modifies the association factors (X 1 ) to account for the lack of aluminum (Al) and potassium (K) measurements, as described by the following relationship:
- the two calculations may be checked against one another. Thereafter, the elemental concentration determined based on absolute yields may be combined with the elemental concentration determined based on relative yields and oxide closure to obtain a weighted mean of the results. This weighted mean may have constant weight or a confidence-estimate-adjusted weight.
- the comparison of the elemental concentrations based on relative yields and closure with the elemental concentrations based on absolute yields may also be used to determine the scaling factor f, by forcing the two derived concentrations to agree in known or simple zones, or over a large portion of the total measured region.
Abstract
Description
Claims
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BRPI0914131A BRPI0914131A2 (en) | 2008-06-25 | 2009-06-29 | system, and method |
CA2729550A CA2729550C (en) | 2008-06-25 | 2009-06-29 | Absolute elemental concentrations from nuclear spectroscopy |
AU2009267178A AU2009267178B2 (en) | 2008-06-25 | 2009-06-29 | Absolute elemental concentrations from nuclear spectroscopy |
CN2009801257335A CN102084271B (en) | 2008-06-25 | 2009-06-29 | Absolute elemental concentrations from nuclear spectroscopy |
US12/996,533 US10061055B2 (en) | 2008-06-25 | 2009-06-29 | Absolute elemental concentrations from nuclear spectroscopy |
GB1101020.4A GB2473994B (en) | 2008-06-25 | 2009-06-29 | Absolute elemental concentrations from nuclear spectroscopy |
MX2011000008A MX2011000008A (en) | 2008-06-25 | 2009-06-29 | Absolute elemental concentrations from nuclear spectroscopy. |
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RU2011103537/28A RU2502095C2 (en) | 2008-06-25 | 2009-06-29 | Absolute elemental concentrations from nuclear spectroscopy |
NO20110035A NO342144B1 (en) | 2008-06-25 | 2011-01-11 | Absolute elemental concentrations from nuclear spectroscopy |
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Publication number | Priority date | Publication date | Assignee | Title |
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WO2011133363A2 (en) | 2010-04-21 | 2011-10-27 | Schlumberger Canada Limited | Neutron porosity downhole tool with improved precision and reduced lithology effects |
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CN103744121B (en) * | 2013-10-28 | 2017-08-25 | 王振信 | Method for logging well by saturability of C/H ratio to stratum fluid |
CN103696765B (en) * | 2013-11-06 | 2016-08-17 | 中国石油大学(华东) | Double LaBr based on controllable neutron source3detector elements spectrometer tool and logging method |
GB201322365D0 (en) * | 2013-12-18 | 2014-02-05 | Commw Scient Ind Res Org | Improved method for repid analysis of gold |
CN104329075B (en) * | 2014-09-05 | 2017-01-18 | 西安奥华电子仪器股份有限公司 | Obtaining method of element capture normal spectroscopy in elemental logging |
CN107229080B (en) * | 2017-05-23 | 2018-07-20 | 兰州大学 | A kind of acquisition methods of geochemical well logging neutron absorption gamma spectra |
CN108171035A (en) * | 2017-08-08 | 2018-06-15 | 王俊芝 | Big data processing platform |
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Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4760252A (en) * | 1983-06-28 | 1988-07-26 | Schlumberger Technology Corporation | Well logging tool with an accelerator neutron source |
US5804820A (en) * | 1994-09-16 | 1998-09-08 | Schlumberger Technology Corporation | Method for determining density of an earth formation |
US20020130258A1 (en) * | 2001-03-14 | 2002-09-19 | Odom Richard C. | Geometrically optimized fast neutron detector |
US20020170348A1 (en) * | 2001-05-18 | 2002-11-21 | Roscoe Bradley A. | Well logging apparatus and method for measuring formation properties |
FR2883596A1 (en) * | 2005-02-28 | 2006-09-29 | Schlumberger Services Petrol | Well logging tool has gamma-ray detector on support and spaced from neutron source, and shielding material between gamma-ray detector and neutron source |
Family Cites Families (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3943362A (en) * | 1974-01-18 | 1976-03-09 | Texaco Inc. | Simultaneous oxygen and silicon neutron activation well log using pulsed neutron source |
US5021653A (en) * | 1990-02-07 | 1991-06-04 | Schlumberger Technology Corporation | Geochemical logging apparatus and method for determining concentrations of formation elements next to a borehole |
CN1047237C (en) * | 1993-08-09 | 1999-12-08 | 清华大学 | Carbon/oxygen energy spectrum logging system |
US5539225A (en) * | 1994-09-16 | 1996-07-23 | Schlumberger Technology Corporation | Accelerator-based methods and apparatus for measurement-while-drilling |
US5699246A (en) * | 1995-09-22 | 1997-12-16 | Schlumberger Technology Corporation | Method to estimate a corrected response of a measurement apparatus relative to a set of known responses and observed measurements |
RU2092876C1 (en) * | 1996-12-30 | 1997-10-10 | Научно-техническое товарищество с ограниченной ответственностью фирма "Геокон" | Radioactive logging process and device |
CN1206837A (en) * | 1997-03-04 | 1999-02-03 | 安娜钻机国际有限公司 | Method for measuring earth stratum density |
CN1375708A (en) * | 2002-01-31 | 2002-10-23 | 殷国才 | Boron neutron injectino-gamma saturation logging method |
CN100492055C (en) * | 2003-09-10 | 2009-05-27 | 中国石油集团测井有限公司技术中心 | A chlorine spectrometry logging method |
RU2262124C1 (en) * | 2004-05-26 | 2005-10-10 | Закрытое акционерное общество Научно-производственная фирма "Каротаж" (ЗАО НПФ "Каротаж") | Method for pulse neutron logging and device for realization of said method |
-
2009
- 2009-06-29 CA CA2729550A patent/CA2729550C/en not_active Expired - Fee Related
- 2009-06-29 AU AU2009267178A patent/AU2009267178B2/en not_active Ceased
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Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4760252A (en) * | 1983-06-28 | 1988-07-26 | Schlumberger Technology Corporation | Well logging tool with an accelerator neutron source |
US5804820A (en) * | 1994-09-16 | 1998-09-08 | Schlumberger Technology Corporation | Method for determining density of an earth formation |
US20020130258A1 (en) * | 2001-03-14 | 2002-09-19 | Odom Richard C. | Geometrically optimized fast neutron detector |
US20020170348A1 (en) * | 2001-05-18 | 2002-11-21 | Roscoe Bradley A. | Well logging apparatus and method for measuring formation properties |
FR2883596A1 (en) * | 2005-02-28 | 2006-09-29 | Schlumberger Services Petrol | Well logging tool has gamma-ray detector on support and spaced from neutron source, and shielding material between gamma-ray detector and neutron source |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2011133363A2 (en) | 2010-04-21 | 2011-10-27 | Schlumberger Canada Limited | Neutron porosity downhole tool with improved precision and reduced lithology effects |
EP2548053A2 (en) * | 2010-04-21 | 2013-01-23 | Schlumberger Technology B.V. | Neutron porosity downhole tool with improved precision and reduced lithology effects |
EP2548053A4 (en) * | 2010-04-21 | 2013-10-30 | Schlumberger Technology Bv | Neutron porosity downhole tool with improved precision and reduced lithology effects |
US9372277B2 (en) | 2010-04-21 | 2016-06-21 | Schlumberger Technology Corporation | Neutron porosity downhole tool with improved precision and reduced lithology effects |
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BRPI0914131A2 (en) | 2015-10-20 |
GB2473994A (en) | 2011-03-30 |
CA2729550A1 (en) | 2010-01-07 |
AU2009267178B2 (en) | 2015-03-12 |
CA2729550C (en) | 2017-02-14 |
NO20110758A1 (en) | 2011-01-31 |
WO2010002796A3 (en) | 2010-12-09 |
NO20110035A1 (en) | 2011-01-31 |
MX2011000008A (en) | 2011-02-24 |
GB201101020D0 (en) | 2011-03-09 |
GB2473994B (en) | 2013-03-20 |
RU2011103537A (en) | 2012-08-10 |
AU2009267178A1 (en) | 2010-01-07 |
RU2502095C2 (en) | 2013-12-20 |
NO342144B1 (en) | 2018-03-26 |
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CN102084271A (en) | 2011-06-01 |
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